734 



MR. C. TATE REGAN ON 

 Text-%. 115. 



[June 1 9, 



Mandibular and h3'^oid arches of a Plenrotreme (A) and a Hypotreme (B). 



A. Squatina angelus (after Gegenbaur). B. Haia clavata (after Parker). 



jot, pterygo-quadrate ; p, palato-basal process ; in, meckelian cartilage ; /;, hyo- 

 maudibular; c, cerato-lij'al ; b, basi-hyal; r, cartilaginous brancbiostegal 

 rays. 



minant. These terms have no practical application ; both groups 

 include types in which the secondary calcification of the vertebral 

 centra has no laminar structure (e. g. Hhynchobatus, Oxyrhina), 

 and others in which it is deposited as a series of concentric 

 laminfe [Squatina, Getorhinus) ; also in both are forms in which 

 the calcification presents a radiating pattern in cross section 

 (e. g. Narcine, Orectolobus). 



In order to arrive at a natui-al arrangement of the Euselachii 

 I have studied at any rate the more important of the numerous 

 memoirs dealing with their anatomy, and wherever possible, and 



